This invention relates generally to gas turbine components, and more particularly to turbine shrouds and related hardware.
It is desirable to operate a gas turbine engine at high temperatures for efficiently generating and extracting energy from these gases. Certain components of a gas turbine engine, for example stationary shroud segments and their supporting structures, are exposed to the heated stream of combustion gases. The shroud is constructed to withstand primary gas flow temperatures, but its supporting structures are not and must be protected therefrom. To do so, a positive pressure difference is maintained between the secondary flowpath and the primary flowpath. This is expressed as a back flow margin or “BFM”. A positive BFM ensures that any leakage flow will move from the non-flowpath area to the flowpath and not in the other direction.
In prior art turbine designs, various arcuate features such as the above-mentioned shrouds, retainers (referred to as “C-clips”), and supporting members are designed to have matching circumferential curvatures at their interfaces under cold (i.e. room temperature) assembly conditions. During hot engine operation condition, the shrouds and hangers heat up and expand according to their own temperature responses. Because the shroud temperature is much hotter than the hanger temperature and the shroud segment is sometimes smaller than the hanger segment or ring, the curvature of the shroud segment will expand more and differently from the hanger curvature at the interface under steady state, hot temperature operation conditions. When the engine is at operating conditions, the C-clip (which is applied at room temperature during assembly, usually with a pre-loaded interference fit) expands to allow thermal deformation in the mating hardware. Stress is induced in the C-clip and mating hardware as the thermal deformation increases. The larger the thermal gradients the larger the stress and the higher the risk of part failure and cracking, lowering the operational life of the C-clip. The thermal deformation can also result in gaps in the shroud assembly which increases undesired leakage, reducing BFM.
Accordingly, there is a need for an assembly that can reduce the curvature deviation effects on the C-clip at the hot operation condition, minimizing the adverse impact to the C-clip, shroud, and hanger durability.